thanks friends! yeah ischa im glad you promptly said "no" to the mirror base. this became so much better although it required a good 10hr+ work...
the marble is pretty easy to make, but then i guess many things are when you know how. it is primed and painted pure white for a start, then i used a sponge with dilluted (codex) grey. the dilution ratio was different so the pattern was not equally strong all over. i deliberately made tidemarks, and afterwards some was enhanched with a brush afterwards, painting some "veins".
then glazed with a mix of gw's old midnight blue and vallejo smoke, creating a green-ish colour. highlighted white. hmm... too bad i didnt make a step by step...